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Review Problems – Incomplete Dominance
Be sure to show your work (Punnett square).
In mice, incomplete dominance exists between the fur colors black and white are. Black
fur color is represented by the alleles BB, and white fur color is represented by the alleles
WW. If a mouse is gray, its alleles are BW. (Use this information to answer questions 13).
1. Cross two mice, one having black fur, the other having white.
Genotypes:
Phenotypes:
2. Cross two mice, one having black fur, the other having gray fur.
Genotypes:
Phenotypes:
3. Cross two mice, both having gray fur.
Genotypes:
Phenotypes:
4. How many chromosomes does a person have _______.
5. How many pairs of chromosomes does a person have _____.
6. What number of chromosomes is in a human sperm cell _____.
7. What number of chromosomes is in a human egg cell _____.
8. What number of chromosomes appears in a human fertilized egg cell (a zygote) ____.
9. What 2 letter chromosomes make a zygote develop into a female in humans _____.
10. What 2 letter chromosomes make a zygote develop into a male in humans _____.
Fruit flies show incomplete dominance in body color. Black body color is represented by
BB, and brown body color is represented by RR. If a fly inherits the B and R alleles for a
genotype of BR, that fruit fly’s body color is striped. (Answer questions 11 -14 using this
information).
11. Cross a black fly with a striped fly.
Genotypes:
Phenotypes:
12. Cross a black fly with a black fly.
Genotypes:
Phenotypes:
13. Cross a brown fly with a striped fly.
Genotypes:
Phenotypes:
14. Cross two striped flies.
Genotypes:
Phenotypes:
Genetic crosses work best when working with organisms that have large numbers of
offspring that can reproduce very quickly. For the following list of organisms, number from
1 to 5, 1 being the best organism to use for genetic research, and 5 being the worst organism
to use for genetic research.
_____. Humans usually have one child at a time, and currently an average of 2.7 children in
a life time.
_____. Mice usually have about 10 offspring at a time, and about 12 litters a year.
_____. Some bacteria can reproduce every twenty minutes to create billions of new bacteria
in a short time (Hours).
_____. Dogs usually have about 6-7 offspring, and about 1-2 litters a year.
_____. Mature Oak trees usually produce about 500 to 1,000 acorns each year.
Ratios: To set up ratios, rather than percents, simply use the actual numbers from your
Punnett square.
For example: If the result of your Punnett square is 3 black and 1 brown, the ratio of black to
brown is 3:1. (We could also express this as 75%:25%).
Use ratios to show the offspring from your Punnett squares in questions numbers 1-3, and
11-14.
1.
12.
2.
13.
3.
14.
11.
Challenge:
Cross a mouse homozygous for Orange fur and having blue eye, with a mouse having red fur
and homozygous for Brown eyes. (Show all you’re work).